Timing apparatus



Fig. 1.

Oct. 7, 1941. L. G. LEVOY 2,258,253

TIMING APPARATUS Filed Aug. 5, 1958 SSheets-Sheet l lmv entor: Louis 6. Levog,

,v 63 W by Hi; Attorney.

Oct. 7, 1941.

I HIIIIIIFI 1.. (a. LEVOY 2,258,253

TIMING APPARATUS Filed Aug. 5, 1938 3 Sheets-Sheet 2 Fig. 4'.

Fig.5.

' Inventor: Louis 6. Levog,

b His Att 3rhg Oct. 7, 1941. L. G. LEVOY 2,253,253

TIMING APPARATUS Filed Aug. 5, 1938 Z Sheets-Sheet 3 Fig.9.

His Attorne g.

Patented Oct. 7, 1941 TIMING APPARATUS Louis G. Levoy, Ballston Lake, N. 1., assignor to v General Electrical Company, a corporation of New York Application August 5, 1938, Serial No. 223,258

14 Claims.

My invention relates to timing apparatus and more particularly to repetitive timing apparatus for use in systems where the precise timing of the supply of current to a load from a source of alternating current during predetermined half cycles or portions thereof is required.

It is an object of my invention to provide new and improved apparatus having utility wherever regular or irregular timing patterns requiring precise timing, as in welding systems, are desired and which is flexible. simple and emoient.

It is a further object of my invention to pro vide improved timing mechanism of the type clescrlhed which is particularly adapted to provide repetitive timing patterns.

L; is also an object oi my invention to provide improved timing apparatus which is readily and economically manufactured and installed.

Still another object of my invention is to provide improved apparatus for precisely controlling the flow of alternating current in a load circult.

It is still another object of my invention "to provide new and improved apparatus for permitting alternating current to flow in a load circuit only during certain particular half cycles or por= tions thereof.

it is another object of my invention to provide a new and improved control element particularly adapted for use with resistance welding or similar apparatus, especially in seam welding operations.

Further objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of my invention reference may be had to the accompanying drawings in which Fig. 1 is a plan view of apparatus embodying my invention; Fig. 2 is a side elevational view, partly broken away, of the apparatus illustrated in Fig. 1; Fig. 3 is an enlarged view, partly in section, of a portion of the chain and buttons shown in Figs. 1.- and 2; Fig. 4 is an end view of the detail shown in Fig. 3; Fig. 5 is a detail of my invention; Fig. 6 is an end view of a chain as shown in Fig. 1 equipped with special links; Fig. 7 is a side view of the apparatus shown in Fig. 6; Fig. 8 is a view in perspective of one of the special links illustrated in Figs. 6 and '7; Fig. 9 is a suitable circuit which may be employed in applying my invention to a welding system; Fig. 10 is an auxiliary circuit which may be used to give greater flexibility of operation; Figs. 11 and 12 illustrate certain operating characteristics of the circuit shown in Fig. 9; and Fig. 13 illustrates a special link also shown in the chain of Figs. 6 and 7.

I have provided a master control element which may be employed in systems where precise timing of the supply of current to a load from a source of alternating current during predetermined hall cycles or portions of half cycles of the source in order to control a sequence oi electrical or mechanical or both electrical and mechanical operations. This control element comprises a supporting element ill such as a longitudinally extending strip in the form of a hell; or chain, for example, and, for convenience generally "termed a helt" hereinafter, preieralily of the endless type, to which suitable open sting members "22 are attached. For controlling electric circuits 1 have provided means on the hell; or chain l5 to vary the flow of current within an electric control circuit. In the embodiment 01' my invention herein described, 35 provide a chain if) in which the links or the chain carry extended pins is arranged to receive "the operating members 22 which may he buttons or blocks, preferably removable, of either insulating or conductive material; Circuit means such as a conducting strip or brush 28 is provided to make electrical contact with the buttons as the huttons or members are carried into the vicinity of the circuit means, ior example, are driven past the hrush. it will be apparent that a control circuit including the buttons and the brush will he completed when the brush is in contact with a conducting button. Accordingly, the positions of the conducting blocks 22 on the chain determine the timing pattern and the rate at which the buttons pass a fixed reference point will determine the timing of the pattern. Instead of an electrical pick-up including a brush other means to apply a predetermined timing pattern for controlling an electric circuit may be used as, for example, magnetic, electrostatic or photoelectric pick-up arrangements.

By employing auxiliary brushes and operating arms 33, my invention may be employed not only to time the occurrence of the predetermined cycle of events but may be used to control any desired auxiliary operations as a counting device, i'or example, or to start and stop any associated apparatus. Other applications of such a mechanism will readily occur to those skilled in the art.

In resistance welding systems of certain types the current is applied intermittently and in such apparatus it is advantageous to be able to simply and quickly change the particular welding cycle to any other cycle without the necessity or inconvenience of gear changing. In such an application, I contemplate the employment of my invention to control the excitation of a circuit adapted to supply current to an electric welder. A suitable supply circuit includes a pair or reversely-connected electric valves 53 (see Fig. 9) and includes means to select the particular interval of time such as a half cycle, cycle or group 01 cycles during which the valves are rendered conductive and also the instant in the chosen halt cycle, cycle or group of cycles at which the valve becomes conductive. This means includes in the illustrated embodiment an endless chain I l which passes over a sprocket l3 driven at a predetermined average rate as, for example, through a speed-changing device by a synchronous motor IO. If the motor is arranged to drive the chain at a speed such that 2) buttons or blocks pass a given stationary point per second, where f is the irequency of the alternating current motor supply, each block or operating member will represent one-half cycle. It control in steps 01' one cycle is suflicient, the speed may be such that 1 members pass the reference point per second instead of 2 members. In other words, each block or member represents a whole cycle instead of a half cycle.

Any suitable means may be provided on the chain to enable the user to prepare the chain for controlling the above referred to circuit. I prefer to use the above-mentioned circuit controller and brush arrangement. With this arrangement the particular half cycles during which the valves will be rendered conductive will depend upon the position in the chain of the conducting links. This mechanism will accomplish anything required in modern welding cycles with no gear changes. Any number of complete cycles may be set up since the chain'can be almost any length.

I also intend to use special indexing or signal links 32 for such purposes as indexing irregular timing patterns, changing the effective heat for different groups of speeds in any desired sequence, and so on, as will occur to those skilled in the art.

In order to select the particular instant in the desired half cycle at which the valves become conductive, I intend to employ a suitable phase shifting circuit, illustrated herein as exciting a peaking transformer thereby producing peak voltages of variable phase.

In the specific embodiment of my invention herein illustrated and described, I have provided a synchronous motor ill supported from the base II by means of vibration absorbing D ds l2. The motor i is arranged to drive a sprocket l3 through a suitable system oi gears included within the gear box H. The gears are selected so that the motor ill will drive the sprocket I 2 at such a speed that the product of the number of sprocket teeth and the speed in revolutions per second of the sprocket is equal to 2 where j is the frequency of the supply system in cycles per second assuming that half cycle control is desired. Ii cycle control is to be employed, the speed in revolutions per second of the sprocket l3 need only be half as great as when half cycle control is employed. In other words, for half cycle control, assuming a 60 cycle supply voltage, 120 blocks should pass the reference point each second while for cycle control only 60 blocks per second will be required to give the necessary control. Sprocket i2 is adapted to drive an endless chain II of the roller or bushing type except that the pins ll connecting the links or the chain are extended as indicated in Fig. 3. The length of the chain is determined by the length of the work cycle, since one link or one circuit controller button must be provided for each half cycle in the work cycle.

In order to keep the chain it taut during operation of the mechanism I provide an idler sprocket I1. I have found that in most cases it is unnecessary to provide any support for the idler sprocket l'l other than the chain II. However, if an unusually long chain is employed, there may be some whip present or it the floor is not level, the apparatus may be tipped in such a direction that the chain will tend to fly of! the driving sprocket ii. In such cases, I provide a bearing II for the sprocket IT, as shown in Fig. 5,

. which is carried by a bracket IO adapted to slide on a guide 20 which may be attached at its upper end to base l-l. Ordinarily, the weight of the bracket l9 and sprocket I1 is sufllcient to keep the chain taut but I have provided clamp 2| so that the bracket I! may be secured against vertical movement whenever desired. When chains of different lengths are to be interchangeably used, it is advantageous to employ a bracket I! which is permitted to slide on the guide 20 because of the saving in time which might otherwise be required for loosening and re-tightening clamp 2| The buttons 22 which are employed in constructing the circuit controller, as best illustrated in Figs. 3 and 4, are drilled as indicated at 22 to receive the pins II and provided on the outside with an annular groove deepened on one side as indicated at 25 for reception 0! a spring clip 28 which is arranged to engage an annular groove 21 in the pins ll. Thi arrangement permits ready removal and placement or the buttons or blocks 22 while insuring a firm engagement with the pins. Conducting material, such as iron or brass, is used for at least a portion 0! the members representing those intervals of time in which it is desired to render the valves conducting while a button or block of relatively nonconducting or insulating material, such as a nonmetallic resinous substance, will be applied to the chain corresponding to those portions of the cycle in which it is desired to maintain the valves non-conducting.

I have provided a brush contact element 2| to engage the buttons or blocks 22 01' the circuit controlling device. As best seen in Figs. 1 and 3, the blocks or members 22 are arranged closely adjacent the members on either side so that a substantially continuous or smooth surface is presented to the brush or electrical contact element 28. This brush is supported in a brush holder 20. Contact with the external control circuit is made through a clamping screw 30 and a terminal 20a. The holder 28 may -be secured to the ar box ll or in any suitable manner. I have provided means for properly positioning the brush 28 to minimize sparking between the brush 28 and the buttons 22. This may be done either by adjusting the extent to which the brush 28 projects from the block 29, after ilrst loosening the screw 30, or else by setting brush 2! in a suitable position and turning slightly the sprocket II on its shaft. After the best position for minimum sparking is determined, an indicator II is suitably secured to indicate the proper position oi the brush. Thereafter as wear of the brush occurs the brush 28 may be moved to the proper position indicated by the indicator 3!. Adjustment may also be obtained by turning the sprocket with respect to its shaft.

The steps in setting up the welding cycle will now be briefly described. Assuming that the speed of the apparatus is such that each block represents a half cycle of the supply current, if only conducting blocks are used, current will be supplied to the welder during each half cycle. However, it is more usual to require the intermit tent application of current. For example, suppose that it is desired to render the tubes conductive for two half cycles, non-conductive for three half cycles, conductive for two half cycles, non-conductive for three halt cycles, and repeat. Two conducting blocks will be snapped into place on successive pins 18. Insulating buttons will be inserted on the three pins next following and so on until the cycle is completed. Since the cycle is to be repeated after the second group of three insulating buttons is applied, the operator will add two conducting buttons, three insulating buttons and so on. When the complete cycle has been set up, the last link is joined to the first link to complete the endless chain. It will be apparout to those skilled in the art that anti-polar or uni-polar starting may be had by arranging the conducting members in a suitable sequence.

The connecting links I05, as shown in Fig. l have two pins it, one at each end, and each link N15 is empolyed to join roller or bushing links I06 by means of pins l8. In order to provide a chain in which there is a minimum of backlash or play between the parts or links thereof and thereby retain the members sumciently firmly so that precision control of the welding circuit is made possible, the roller or bushing elements separat ing and spacing the links i522 and I36 closely fit the pin it and 503. Moreover, the openings in the links loll, 55a and i522 also closely lit the pins passing therethrough. Ii the links M5 are used throughout, an even number of buttons must be used. It may happen, however, that an odd number of members or buttons is desired. For such a case, auxiliary connecting links lfl'l, as shown in Figs. 13, 6 and 7, are provided. Auxiliary links it? are ll-shaped and similar to con necting links 306 at one end, but the side pieces I08 are spread out or offset at the opposite end to lit the end of. a link I06. A. pin I09, similar to pins I6, is run through openings in arms H18 and link Hi6 to provide one additional block hold ing pin.

In many instances it may be desirable to control some auxiliary operation. For instance, it may be desirable to change the speed at which the work is advanced to the welding electrode or it may be desired to change the amount of heat during the welding cycle. For any such purpose I have provided special links or cover plates 32 having offset ears or lugs 32a arranged for carrying pins or arms 33 as shown in Fig. 7. It will be understood that special links 32 are interchangeable with the cover plates or links I5a or I511 01 the chain 15. It will also be apparent that the chain can be assembled with links l5a and Nb, Fig. '1, as separable parts of the chain to provide the maximum degree of flexibility. These pins 33 are adapted to engage auxiliary brushes 34 which may be suitably connected into an auxiliary circuit as will be described later. While in Fig. 8 I have shown a special link 32 carrying a single pin 33, it will be apparent that any number of pins might be provided for. Furthermore, it is not necessary that pins 33 extend beyond the faces of blocks 22 as shown in Fig. '7. As indicated in Figs. 6 and 7, these auxiliary signals may be carried on either orboth sides of the chain. If desired, a special link might be employed having extensions on both sides of the chain. Fig. '7 indicates a suitable brush rigging for these special links. A brush 28 is shown for engagement with the circuit controller buttons while two auxiliary brushes 34b and 340 are shown below brush 28 to engage auxiliary pins 33b and 330, the latter not being shown in the drawing, respectively, below the commutator blocks and two similar auxiliary brushes 34 and 34a are arranged above the main brush 28 for engagement with pins 33 and 33a, respectively, carried outside the circuit controller blocks 22. In some instances, it may be desirable to have a very slight time delay in the initiation of a certain operation, for example, it may be desired to use a signal to index the welding cycle or, in other words, to provide a contact finger or arm and auxiliary brush to prevent operation of the welder until the proper portion of the cycle is reached and to begin spot welding immediately thereafter, that is, within the first half cycle after reaching the indexing point. This can be accomplished by staggering a pair of pins 33 on one of the special links 32, that is, by placing one of the pins 33 close to the leading edge of the special link while a second pin 33 will be placed near the lagging edge of the special link, each of the pins or arms 33 engaging a suitable auxiliary brush 34. Qther uses for auxiliary signals will be readily apparent to those skilled in the art.

A suitable circuit for controlling the operation of the above described application of my invention is shown in Fig. 9. An alternating current supply circuit 50 is connected to the load, a welding circuit 55 in the illustrated embodiment, through a transformer 52 and a pair of reverselyconnected electric valves 53 which are connected in series relation with the primary 5d of the welding transformer 52. The electric valves 53 are preferably of the type using an ionizable gas or vapor and include an anode 55, a cathode 56,

and a control member 51 which may be of the make alive or immersion ignitor type.

In order to control the energization of the control members 51, i have provided excitation circuits which are associated with the valves 53. The excitation circuits are similar in construction and arrangement and for the remaining de-= scription of the circuits I will describe but one of the excitation circuits. It will be understood, however, that the second excitation circuit operates in a similar manner, corresponding parts of each circuit being represented by the same numerals. A control electric valve S0 is provided in each excitation circuit in order to effect the energization of the control member 51 of the valve 53 at the proper times and during predetermined intervals. The control electric valve 60 is preferably of the type employing an ionizable medium and is provided with an anode 6|, a cathode 62 and a control member 63 which may be of the grid type. The anode of the control electric valve 60 is connected to the anode 55 of the electric valve 53 through a current limiting resistor 64. The cathode of the control electric valve 60 is connected to the control member 51 of the electric valve 53.

I have provided means for introducing into the excitation circuit a biasing potential tending to maintain the control electric valve non-conducting. For this purpose, a transformer 65 having a primary 66 is connected across the supply lines 50. The voltage appearing at the terminals of the secondar winding 61 of the transformer 65 is rectified by means of a half wave rectifier 68 and applied b the excitation circuit across a condenser 10.

In order to introduce into the excitation circuit an applied voltage such as a predetermined number of half cycles of alternating current voltage which tends to render the valve 60 conducting I provide a transformer H having a primary 12 and secondaries 13 each of which is connected in series with the bias voltage across each condenser 10. A resistance 13a is connected across each secondary 13 to by-pass any high frequency surges appearing in the grid circuit and also to improve the power factor of transformer II. In order to energize the primary 12 of transformer II I have provided a circuit including the circuit controller and chain l described above and a source of alternating current voltage. This source of voltage is derived from the secondary 68 of the transformer 65. The energization of primary 12 of transformer II is intermittent, the sequence and duration of the period being governed by the arrangement of conducting segments on the circuit controller. A resistor H in series with the primary I2 and a capacitor I5 connected in parallel with the primary 12 of transformer H are provided in order to smooth out any transients which may have developed in the circuit due to the make and break between brush 28 and the conducting buttons or blocks in the circuit controller. The above described means for suppressing transients caused by the circuit controller or make-and-break device is described and claimed in my copending application Serial No. 316,863, filed February 1, 1940, and assigned to the same assignee as the present invention. Lead Ha is shown as grounded. This ground connection is most conveniently made to the motor frame. The magnitude of the alternating current voltage in the excitation circuit occasioned by the voltage obtained from secondary 13 of transformer H is insufiicient to overcome the negative bias due to the rectified current. Referring to Figs. 11 and 12 the D. C. l

bias applied across condenser is indicated at l6 while the alternating current voltage derived from secondary 73 is indicated by the curve 11. The anode voltage is represented by the curve 18. It is apparent from these curves that the sum of voltages 16 and 11 is at all times insufficient to render the control member 83 of the tube 50 sufficiently positive to render the electric valve 60 conductive.

In order to render the electric valve 60 conductive I provide for the introduction of a second alternating current voltage to cooperate with the first alternating current voltage during predetermined intervals of time established by the voltage obtained from transformer II. This voltage is obtained from secondary winding 19 of a peaking transformer 80 the primary of which is energized from phase shifting circuit 82. In order to impress an alternating current voltage on primary 8| of transformer 80 of apredetermined phase relationship relative to the voltage of the supply circuit and hence to control the amount of energy transferred to the load, I employ a phase shifting circuit 82 comprising a capacitor 83 and a variable resistor 84. The primary ll of the transformer 00 is energized through the phase shifting network 82 and the primary 88 of the transformer 85, the circuit including a current limiting resistor 85, reactor '0 and capacitor 81. Reactor 86 and capacitor 81 constitute a tuned filter, the purpose of which is to prevent tooth harmonics or any other small distortion of the alternating current wave from affecting the narrow peaks generated in the secondary 19 of transformer 80. The peaks from the peaking transformer appear in the grid circuit of the control electric valve ill as represented by the numeral 88 in Figs. 11 and 12. As indicated by Fig. 11 the magnitude of the peak is insufficient to render the control electric valves conducting in the absence of the voltage developed in secondary 13 of transformer 1|. However, when transformer II is energized, the effective bias on the control member 63 is reduced so that the effective voltage applied to control member 63 of electric valve 80 is suflicient to render the control electric valve 50 conductive.

I have shown an auxiliary control circuit in Fig. 10 which may be used for indexing irregular timing patterns, as for example for changing the effective heat for different groups of spots in any desired sequence or cycling the pressure to the weld. The circuit is provided with power, direct current in this exemplification, over a positive main 90 and a negative main 8! for the energlzation of any desired number of signal elements. I have illustrated three translating devices or signal elements 92, 93 and 94 which may be relays, windings on a saturable reactor, direct current windings for shifting the phase of a peaking transformer or any other desired translating device. In order to control the energize.- tion of the translating devices 82, 93 and 94 I have provided excitation circuits including control electric valves 95, 95a and 85b. The control electric valves are preferably of the type employing an ionizable medium and each is provided with an anode 95, a cathode 91 and a control member 98. The cathode 91 of the electric valves are connected to a tap I00 on the potential divider 99 connected across the D. C. supply source 90, 8| in order to maintain the control elements 98 of the electric valves normally negative with respect to the cathodes 91.

In order to vary the bias applied to the control elements 98 for rendering the electric valves 95 conductive, any suitable means may be used. I have shown the use of auxiliary brushes 34, 34a, and 34b adapted to engage signal arms 33, 33a and 33b extending from chain l5 as referred to above although any type switch circuit closing means may be used. These brushes preferably make momentary contact with the respective auxiliary or signal pins to trigger the associated electric valve.

In order that the ignition of one electric valve will extinguish any other electric valve which has been conducting previously, I have provided capacitors I02, I03 and I04.

The condensers are connected between the excitation circuits so that when one of the electric valves fires, as when brush 34 engages pin 33 to fire valve 95, all condensers will be charged. If, at a later time, a second brush as a engages its associated pin 330. the grid of the second tube is driven positive, momentarily. with respect in its cathode thereby rendering valve 85a conductive. This action drives anode 06 of valve 85 negative with respect to its cathode 81 by reason oi the discharge of condenser I02, thereby extinguishing valve 05.

, current energizes signal element 02 and charges capacitors I02, I03 and I04 as follows. Alter valve 95 becomes conducting practically the entire voltage drop between tap I and the positive lead 90 appears across device 02 since the arc drop in valve 95 is comparatively small. Therefore, the anode 98 of valve 95 will be at a potential different from that of the cathode 91 only by the amount of the arc drop. Condenser I02 may be considered as being connected in a series circuit from the tap I00 of potential divider 99 through valve 95, capacitor I02 and device 93 to the positive lead 90. Thus voltage is applied across capacitor I02 to charge the same. Capacitor I03 is similarly charged through signal member 94 and valve 95, and capacitor I04 is charged through signal element 94, capacitor I02, and valve 95. Assuming that valve 95a fires next, by reason of the engagement of brush 04a and pin 33s that side oi capacitor 302 connected to anode d0 oi valve 95c connected to the cathodeof valve as through the are within valve 95a. Capacitor E02 tends to discharge through valve 85a and. momentarily, cathode 87E of valve 05 hecomes positive with respect to anode 80 of valve 05. Gbviously', valve 96 can no longer con-- duct current and the arc therein is extinguished. Since "crush 30 engaged pin 33 only long enough to trigger valve $5, the circuit including brush 34 and pin 83 is new open and valve 95 remains non-conducting until brush 34 again engages pin 33. Thus, the ignition of electric valve 95a commutates out electric valve 95 by driving its anode 96 negative so that only one valve is conducting at any one time. It will be apparent that when valve 95a became conducting device 93 was error-- gized and device 82 was deenergized. In the same manner, signal element or translating device 94 may be energized and signal element 93 deenergized. this process being repeated in any desired order depending upon the signal pin arrangements. The above-described auxiliary control circuit is described and claimed in my copending application 306,997, filed November 16, 1939, and assigned to the same assignee as my present invention.

Instead of using a brush having sliding contact with the circuit controller blocks, I may substitute a small metal disk spaced a short distance away from the faces of the blocks 22, thus providing a small capacitor in which the conducting blocks act as one plate of the condenser and the small metal disk as the other plate. This electrostatic pick-up arrangement amounts to the substitution of a small condenser plate for the brush 28.

A magnetic pick-up is an additional alternative means of control. In this modification permeable and impermeable buttons are used and the control voltage would be obtained from a pick-up coil wound on a magnetic core instead of from the brush and circuit controller arrangement described. A second winding is arranged on the core and separately excited by suitable netic field. As the buttons carried by the chain pass through the magnetic held, the reluctance of the magnetic circuit will be varied according to whether a permeable or impermeable button is passing, thereby varying the amplitude of the voltage in the pick-up coil which in turn is applied to the excitation circuit of the control electric valve. as described above.

With the electrostatic and magnetic arrangements the insulating blocks may be omitted since in the former modification the capacity of the condenser may be varied by increasing the gap between the chain and pick-up plate as the chain moves past the pick-up plate as well as by inserting an insulating block. From another viewpoint, it is just as practical, or perhaps more so, to insert an additional air dielectric as it is to provide some other dielectric material during these periods when the control circuit is to be broken. Similarly, with reference to the magnetic system, it is possible to vary the reluctance of the magnetic circuit by increasing the air gap between the chain and pick-up device as well as by inserting an impermeable block in the magnetic circuit. In both cases the air gap may be increased by omitting the insulating or i permeable buttons.

alternately, instead of providing buttons on the belt or chain, I may use a photoelectric pick up by providing obstructions on the belt or limits of the chain to cut oil? a light beam for con" oi ling an electric circuit as will be obvious to skilled in the art.

It will be apparent that many other modifies. tions of my invention are possible. For exam ple, any sort of belt or tape may he used instead of a chain and any suitable material may he used. @bviously, an endless chain or belt is not acces sary although preferred. Moreover, it is within. the scope of my invention to provide a chem which the links themselves are formed, of either conductive or iusuiative material for the conduc tive pick-up or are formed of various sized. links tor the electrostatic, magnetic, or light sensitive pick-up. Instead of sprockets for driving the belt or chain, I may use any suitable driving mcans.

My invention may be used to initiate not only the supply of current to the welding circuit but also to start, stop and vary the speed of the work advancing mechanisms at predetermined times or close down the welding apparatus after a prescribed cycle has been completed. For example, a resistance welding machine may he used to give a preheating cycle, followed by a welding cycle, followed, in turn by an annealing cycle by proper indexing. In such a case signals could be used to index the pattern so that operation will begin with the preheating cycle, to vary the heat for each spot, as by phase control. and to vary the pressure of the electrodes against the work.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since many modifications may be made both in the circuit arrangement and in the instrumentalities employed, and I therefore contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

I claim:

1. In a timing device for precisely timing the 5 connection of a load to a source of alternating means in order to provide the necessary mag current during predetermined half-cycles of said source, the combination of a belt, a plurality of members carried thereby, the quantity and positions of said members corresponding to the timing pattern desired, means adjacent said belt, and synchronously driven means constructed and arranged for imparting motion to said belt at such a rate that each of said members is associated with said adjacent means during a predetermined relatively short time interval, said belt being adjustable in length for permitting variation of the length the timing pattern.

2. In a timing device for precisely timing the connection of a load to a source of alternating current during predetermined half-cycles of said source, the combination of a supporting element, a plurality of members carried by said supporting element, the quantity and positions of said members corresponding to the timing pattern desired, means adjacent said supporting element, and synchronously driven means constructed and arranged for imparting motion to said supporting element at a rate such that each or said members is associated with said adjacent means during a predetermined relatively short time interval, said supporting member being adjustable in length to permit variation of the length of the complete timing pattern.

3. In a timing device for precisely timing the connection of a load to a source of alternating current during predetermined halt-cycles of said source, the combination of a belt, a plurality of circuit control members carried by said belt, the quantity and positions of said members corresponding to the timing pattern desired, additional circuit control means adjacent said belt and cooperating with said members, and synchronously driven means constructed and arranged for imparting motion to said belt at a rate whereby each of said members is associated with said additional circuit means during predetermined ones of successive and equal time intervals, and auxiliary circuit control means comprising auxiliary members carried by said belt, and additional means adjacent said belt and cooperating with said auxiliary members.

4. In a control system for precisely timing the connection of a load to a source of alternating current during predetermined half-cycles 0! said alternating current, a timing device comprising a supporting element, a plurality of members removably carried thereby, some of said members being formed of an electrically insulative material, other of said members being formed of an electrically conductive material, the number of said members being equal to the number of time intervals utilized during a complete timing pattern and the disposition of said members being determined'by the desired timing pattern, a contact element slidingly engaging said members, and synchronously driven means for causing relative movement between said contact element and said members at the rate of one member for each 0! said time intervals.

5. In a control system for precisely timing the connection 01 a load to a source of alternating current during predetermined time intervals, a timing device comprising a supporting element, a plurality of members removably carried thereby, some of said members being formed from an electrically insulating material, others oi said members being formed from an electrically conductive material, said members being disposed according to a predetermined timing pattern, a contact element arranged to engage said members, and synchronously driven means for imparting motion to one or said elements in order to cause engagement between said elements, said removable members and said supporting element being arranged and constructed so that said members lie closely adjacent the members on either side thereof when assembled on said supporting element in order to present a substantially continuous surface to said contact element.

6. In a timing device for precisely timing the connection of a load to a source of alternating current during predetermined intervals of time, circuit controlling means comprising a belt having a plurality of members removably securedthereto in a predetermined order, some 01' said members being formed from an electrically insulative material, others of said members being formed from an electrically conductive material, the number 01 said members being equal to the number or time intervals utilized during a complete timing pattern, a brush arranged to slidingly engage said members, said belt being synchronously driven and arranged for causing said members to be moved into engagement with said brush at the rate of one member for each of said intervals of time.

7. In a timing device for precisely timing the connection of a load to a source of alternating current during predetermined half-cycles of said source, circuit controlling means comprising a belt having a plurality of members removably secured thereto in a predetermined order, some of said members being formed from an electrically insulative material, others of said members being formed from an electrically conductive material, the number of said members being equal to the number of time intervals utilized during a complete timing pattern, additional switching means including a brush arranged to slidingly engage said members, said belt being synchronously driven and arranged ior causing said members to be moved into engagement with said brush at the rate oi one member for each of said time intervals, said belt being adjustable in length for varying the duration 01' the timing pattern, said belt and said members being so constructed and arranged that said removable members lie closely adjacent when attached to said belt in order to present a substantially continuous surface to said brush.

8. Ina timing device for precisely timing the connection or a load to a source of alternating current during predetermined halt cycles of said source, the combination of a supporting element, a plurality of operating members carried by said supporting element, the quantity and positions of said members corresponding to the timing pattern desired, additional operating means adjacent said belt and cooperating with said members, synchronously driven means constructed and arranged for imparting motion to said supporting element at a rate whereby each of said members is associated with said additional operating means during predetermined ones of successive and equal time intervals, and auxiliary operating means comprising auxiliary members carried by said supporting element and additional means adjacent said supporting element and cooperating with said auxiliary members.

9. In a timing device, a chain comprising separable links, a plurality oi. electric circuit members of electrically conductive material attached to said links at predetermined intervals, an additional electric circuit member adjacent said chain, means for moving said chain to bring said members into association with said additional member, one of said links having an offset portion, contact means attached to said offset portion, and a contact member arranged to engage said contact means when said movement of said chain moves said contact means into proximity with said contact member.

10. In a timing device, a chain comprising separable links, a plurality of electric circuit members of electrically conductive material attached to said links at predetermined intervals, an additional electric circuit member adjacent to said chain, means for moving said chain to bring said members successively into association with said additional member, auxiliary contact means oilset with respect to said chain, and a contact member arranged to engage said auxiliary contact means when said movement of said chain moves said auxiliary contact means into proximity with said contact member.

11. In a control system for precisely timing the connection of a load to a source of alternating current during predetermined half cycles or portions thereof ,of said source, the combination of an adjustable length chain comprising a plurality of separable links, means for connecting together adjacent links, said connecting means and said links being so constructed and arranged that there is substantially no play between adjacent links, each of said connecting means being constructed for removably supporting a member, operating members removably disposed in association with certain of said connecting means, the quantity and positions of said operating members and the length of said chain being chosen according to the timing pattern desired, means adjacent said chain, and synchronously driven means constructed and arranged for imparting motion to said chain at a predetermined average rate in order to carry said operating members into association with said adjacent means in a predetermined order, each of said operating members being in association with said adjacent means during a predetermined time interval.

12. In a control system for precisely timing the supply of current to a load from a source of alternating current during predetermined half cycles or portions thereof of said source, the combination of an adjustable length, substantially rigid supporting element, means associated with said element for removably carrying a plurality of operating members, duplicate operating members removably disposed in association with certain of said carrying means, the quantity and positions of said operating members and the length of said supporting element being chosen according to the desired timing pattern, means adjacent said operating members, means constructed and arranged for imparting motion to said supporting element at a predetermined average rate in order to carry said operating members into association with said adjacent means in a predetermined order, each operating member being in association with said adjacent means during equal and relatively short time intervals.

13. In a control system for precisely timing the supply of current to a load from a source of alternating current during predetermined half cycles or portions thereof of said source, the combination of an adjustable chain comprising a plurality of separable links, means for connecting together adjacent links, said connecting means and said links being so constructed and arranged that there is substantially no play between adjacent links, each of said connecting means being constructed for removably supporting a member, operating members removably disposed in association with said connecting means, some of said members being formed of an electrically insulative material, others of said members being formed of an electrically conductive material, the quantity and position of said operating members and the length of said chain being chosen according to the timing pattern desired, means adjacent said chain and comprising a brush arranged to slidingly engage said members, and synchronously driven means constructed and arranged for imparting motion to said chain at a predetermined average rate in order to carry said operating members into association with said adjacent means in a predetermined order, each of said operating members being in association with said adjacent means during a predetermined time interval.

14. In a control system for precisely timing the supply of current to a load from a source of alternating current during predetermined halfcycles or portions thereof of said source, the combination of an adjustable length chain comprising a plurality of separable links, means for connecting together adjacent links, said means and said links being so constructed and arranged that there is substantially no play between adjacent links, each of said connecting means extending beyond said links, operating members removably disposed on certain of said connecting means, the quantity and positions of said members and the length of said chain being chosen according to the timing pattern desired for the work cycle of said apparatus, means adjacent said chain, and synchronously driven means constructed and arranged for imparting motion to said chain at a predetermined average rate in order to carry said members into the vicinity of said adjacent means in a predetermined order.

LOUIS G. LE'VOY. 

